I was wondering whether the engines of the 346 and 744 could be interchangeable (?)? I mean can you use 4 RR Trent 556 on a 744 or 4 PW 4056 on a 346? My assumption would be, in theory, an absolute yes but, in practice, no because the RR Trent 556 would hang too heavy and low under the wings of a 744? However, PW 4056 could fit perfectly under the wings of a 346 but they would look smallish compared to the RR Trent 556? Can anybody please elaborate more on this topic? Thanks.